The present invention relates to scratch-resistant coatings for plastic optical elements. In particular, the present invention relates to a system and method for large scale production of plastic ophthalmic lenses having a scratch-resistant coating.
Plastic ophthalmic lenses have become increasingly popular because of their lighter weight, reduced bulk and greater shatter resistance than glass lenses. One commonly used monomer system for forming plastic ophthalmic lenses is allyl diglycol carbonate (which is sold under the trademark CR-39).
CR-39 plastic ophthalmic lenses are typically formed by casting the CR-39 monomer in a mold formed by a pair of glass mold pieces connected together by a gasket. The interior of the mold is filled with the CR-39 monomer, and the filled mold is then subjected to a curing process.
CR-39 plastic ophthalmic lenses are relatively hard and scratch-resistant when compared to other plastic ophthalmic lenses. The scratch-resistance of CR-39 lenses, however, is lower than that of glass. As a result, there has been a significant effort expended to develop scratch-resistant coatings for CR-39 and other plastic ophthalmic lenses.
A wide variety of different coating techniques and materials have been proposed over the years. These include applying coating solutions by spin, dip, spray or flow coating. In recent years, considerable effort has been expended in developing "in-mold" coating techniques, in which a coating is applied to a surface of a mold and then transferred to the lens as the lens monomer is cured in the mold.
In the case of spin, dip, spray or flow coating processes, the coating is applied after the CR-39 lens has been cured, and the lens has been removed from the mold.
The glass mold pieces used in casting CR-39 lenses are expensive, and therefore are reused many times before they are replaced. If a glass mold piece has a defect which will cause a lens made with that mold piece to be rejected, it is important that the defective mold piece be identified, removed, and replaced.